The invention pertains to nozzles for directing liquid coolants upon the grinding surfaces of rotating grinding wheels.
It has long been recognized that machining operations accomplished by grinding, i.e., the engagement of a workpiece with a rotating surface of abrasive material, such as Carborundum, can be improved by the generous use of cooling liquids. Accordingly, a wide variety of cooling liquids are available for grinding operations ranging from plain water to sophisticated petroleum products. Most grinding machines, such as centerless grinders, wherein high quality finishes are produced by grinding operations require that the workpiece be flushed with liquid coolant during grinding, and a number of devices have been produced for applying the liquid coolant to the grinding wheel and workpiece.
As the surface of the grinding wheel engaging the workpiece will increase in temperature during the operation, a number of coolant applying devices and nozzles have been produced such as typified by U.S. Pat. Nos. 2,475,811; 2,914,892; 3,256,647 and 3,712,001. One of the purposes of such patents as these is to maintain the maximum amount of cooling liquid upon the grinding wheel periphery to increase the cooling ability of the grinding surface. However, one of the serious problems preventing effective cooling of grinding wheel surfaces is due to the fact that the grinding wheel is rapidly rotating during most conventional grinding applications, and this rapid rotation causes a moving air film to occur immediately adjacent the grinding surfaces which acts as an insulating barrier and shield between the grinding surfaces and the coolant applied to the grinding wheel. The insulating characteristics of air are relatively high, and thus a liberal flushing of a grinding wheel with a liquid coolant is only partially effective in reducing the temperature of the grinding wheel surfaces due to the existence of the surface air film.
It has been proposed to divert this surface air film from the wheel grinding surfaces by the use of mechanical means, such as a doctor blade, and such an arrangement is shown in U.S. Pat. No. 3,325,949. However, such an arrangement, though partially effective, is not capable of completely removing the laminar air film due to the necessary clearance that must exist between the doctor blade and the grinding surface, and the continual change in the diameter of the grinding wheel, due to wear, renders the maintaining of a close dimensional relationship between a doctor blade and the grinding surfaces difficult.
A further difficulty arising from grinding operations results from the presence of minute loose particles which remain on the grinding wheel surface after engagement with the workpiece which are not removed therefrom by the coolant liquid, or the centrifugal forces acting upon the grinding wheel. Such loose particles consist of the metal removed from the workpiece, and particles of the grinding wheel itself, which, during wear, slowly disintegrates. As such small particles remain upon the grinding surfaces, and are successively interposed between the grinding wheel cutting edges and the workpiece, a galling of the workpiece surface occurs which detracts from the quality of the ground workpiece surface, and in instances wherein very high quality ground finishes are necessary, secondary burnishing or grinding operations may be necessary to achieve the quality of finish desired.
In the past, the removal of such loose particles from the grinding wheel grinding surfaces has been limited to liberally flushing the grinding wheel surfaces with coolant liquid endeavoring to wash away such particles. The coolant liquid distribution system usually includes a filter for removing small particles from the coolant liquid, but unless the minute loose particles retained within the voids of the grinding wheel surfaces are removed, optimum ground surfaces cannot be machined.